Support dependent env vars (#390)

* Expand dependent env variables from double curly braces {{ENV_VAR_NAME}} to $(ENV_VAR_NAME)

docs/reference/config-params.md

@@ -700,7 +700,7 @@ All traffic on the port you specify will be forwarded to the service allowing an
 
 Again, it is ideal for exposing a service or app to the internet under a single IP address.
 
-Practically, in non development environments, a LoadBalancer will be used to route traffic to an Ingress to expose multiple services under the same IP address and keep your costs down.     
+Practically, in non development environments, a LoadBalancer will be used to route traffic to an Ingress to expose multiple services under the same IP address and keep your costs down.
 
 
 ## kev.service.nodeport.port
@@ -842,6 +842,21 @@ services:
       ENV_VAR_A: some-literal-value  # Literal value
 ```
 
+When there is a need to reference any dependent environment variables it can be achieved by using double curly braces
+
+> Environment variable with as literal string referencing dependent environment variables:
+```yaml
+version: 3.7
+services:
+  my-service:
+    labels:
+      ...
+    environment:
+      ENV_VAR_A: foo
+      ENV_VAR_B: bar
+      ENV_VAR_C: {{ENV_VAR_A}}/{{ENV_VAR_B}}  # referencing other dependent environment variables
+```
+
 ## Reference K8s secret key value
 
 To set an environment variable with a value taken from Kubernetes secret, use the following shortcut: `secret.{secret-name}.{secret-key}`.

pkg/kev/converter/kubernetes/transform.go

@@ -1250,6 +1250,7 @@ func (k *Kubernetes) configPVCVolumeSource(name string, readonly bool) *v1.Volum
 // @orig: https://github.com/kubernetes/kompose/blob/master/pkg/transformer/kubernetes/kubernetes.go#L961
 func (k *Kubernetes) configEnvs(projectService ProjectService) ([]v1.EnvVar, error) {
 	envs := EnvSort{}
+	envsWithDeps := []v1.EnvVar{}
 
 	// @step load up the environment variables
 	for k, v := range projectService.environment() {
@@ -1347,17 +1348,33 @@ func (k *Kubernetes) configEnvs(projectService ProjectService) ([]v1.EnvVar, err
 				}, "Unsupported Container resource reference: %s", resource)
 			}
 		default:
-			envs = append(envs, v1.EnvVar{
-				Name:  k,
-				Value: *v,
-			})
+			if strings.Contains(*v, "{{") && strings.Contains(*v, "}}") {
+				*v = strings.ReplaceAll(*v, "{{", "$(")
+				*v = strings.ReplaceAll(*v, "}}", ")")
+
+				envsWithDeps = append(envsWithDeps, v1.EnvVar{
+					Name:  k,
+					Value: *v,
+				})
+			} else {
+				envs = append(envs, v1.EnvVar{
+					Name:  k,
+					Value: *v,
+				})
+			}
 		}
 	}
 
 	// Stable sorts data while keeping the original order of equal elements
 	// we need this because envs are not populated in any random order
 	// this sorting ensures they are populated in a particular order
 	sort.Stable(envs)
+
+	// append dependent env variables at the end to ensure proper expansion in K8s
+	for _, de := range envsWithDeps {
+		envs = append(envs, de)
+	}
+
 	return envs, nil
 }
 

pkg/kev/converter/kubernetes/transform_test.go

@@ -1526,6 +1526,25 @@ var _ = Describe("Transform", func() {
 			})
 		})
 
+		Context("for env dependend vars containing double curly braces e.g. {{OTHER_ENV_VAR_NAME}} ", func() {
+
+			secretRef := "postgres://{{USER}}:{{PASS}}@{{HOST}}:{{PORT}}/{{DB}}"
+
+			BeforeEach(func() {
+				projectService.Environment = composego.MappingWithEquals{
+					"MY_SECRET": &secretRef,
+				}
+			})
+
+			It("expands that env variable value to reference dependet variables", func() {
+				vars, err := k.configEnvs(projectService)
+
+				Expect(vars[0].Value).To(Equal("postgres://$(USER):$(PASS)@$(HOST):$(PORT)/$(DB)"))
+				Expect(err).ToNot(HaveOccurred())
+			})
+
+		})
+
 		Context("for env vars with symbolic values", func() {
 
 			Context("as secret.secret-name.secret-key", func() {